U.S. patent number 5,900,384 [Application Number 08/683,269] was granted by the patent office on 1999-05-04 for double metal cyanide catalysts.
This patent grant is currently assigned to Arco Chemical Technology L.P.. Invention is credited to Gerald A. Bullano, Bi Le-Khac, Ahmad Soltani-Ahmadi.
United States Patent |
5,900,384 |
Soltani-Ahmadi , et
al. |
May 4, 1999 |
**Please see images for:
( Certificate of Correction ) ** |
Double metal cyanide catalysts
Abstract
Double metal cyanide catalysts, prepared by drying a catalyst
slurry by a non-agglomerative drying method such as spray drying or
freeze drying, directly produces catalyst particles of fine
particle size such that intensive grinding is not required. The
catalysts thus produced are different from conventionally dried
particles in that polyoxyalkylation may be conducted with less
reactor fouling and a polyoxyalkylene product of lower unsaturation
and narrower polydispersity may be obtained.
Inventors: |
Soltani-Ahmadi; Ahmad (Radnor,
PA), Le-Khac; Bi (West Chester, PA), Bullano; Gerald
A. (Glen Mills, PA) |
Assignee: |
Arco Chemical Technology L.P.
(DE)
|
Family
ID: |
24743284 |
Appl.
No.: |
08/683,269 |
Filed: |
July 18, 1996 |
Current U.S.
Class: |
502/175;
502/200 |
Current CPC
Class: |
B01J
37/0236 (20130101); B01J 37/0045 (20130101); C08G
65/2663 (20130101); B01J 27/26 (20130101) |
Current International
Class: |
B01J
27/26 (20060101); B01J 27/24 (20060101); B01J
37/00 (20060101); B01J 37/02 (20060101); C08G
65/00 (20060101); C08G 65/26 (20060101); B01J
027/26 () |
Field of
Search: |
;502/175,200,159 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wood; Elizabeth D.
Attorney, Agent or Firm: Brooks & Kushman P.C.
Claims
What is claimed is:
1. A process for the preparation of a double metal cyanide complex
catalyst, comprising:
a) preparing a slurry of double metal cyanide complex catalyst
particles in a continuous phase comprising a volatile organic
complexing agent;
b) drying said double metal cyanide complex catalyst particles by
removing said volatile organic complexing agent by a
non-agglomerative drying method; and
c) recovering a powdered double metal cyanide complex catalyst
having a median particle size of less than 40 .mu.m.
2. The process of claim 1 wherein said non-agglomerative drying
method comprises spray drying.
3. The process of claim 1 wherein said non-agglomerative drying
method comprises freeze drying.
4. The process of claim 1 wherein said slurry further comprises a
volatile organic solvent different from said volatile organic
complexing agent.
5. The process of claim 1 wherein said median particle size is less
than about 20 .mu.m.
6. The process of claim 1 wherein said median particle size is less
than about 10 .mu.m.
7. The process of claim 1 wherein said median particle size ranges
from greater than 10 m to less than 40 and further comprising
grinding the powdered double metal cyanide complex catalyst
particles to a smaller median particle size.
8. Double metal cyanide complex catalyst particles comprising the
product produced by the process of:
a) preparing a slurry of double metal cyanide complex catalyst
particles in a continuous phase comprising a volatile organic
complexing agent;
b) drying said double metal cyanide complex catalyst particles by
removing said volatile organic complexing agent by a
non-agglomerative drying method; and
c) recovering a double metal cyanide complex catalyst having a
median particle size of less about than 40 .mu.m.
9. The double metal cyanide complex catalyst of claim 8, wherein
said particles have a median particle size of less than about 20
.mu.m.
10. The double metal cyanide complex catalyst of claim 8, wherein
said particles have a median particle size of less than about 10
.mu.m.
11. The catalyst of claim 8 wherein said double metal cyanide
complex catalyst comprises a zinc hexacyanocobaltate complex
containing t-butanol as a complexing organic agent.
12. The catalyst of claim 11 wherein said zinc hexacyanocobaltate
complex further contains a polyoxyalkylene polyol having a
molecular weight of from about 200 Da to about 10,000 Da.
13. The catalyst of claim 8 wherein said non-agglomerative drying
method comprises spray drying.
14. The catalyst of claim 8 wherein said non-agglomerative drying
method comprises freeze drying.
Description
TECHNICAL FIELD
The present invention pertains to double metal cyanide catalysts.
More particularly, the subject invention pertains to a process for
the manufacture of double metal cyanide complex catalysts which
exhibit unexpectedly improved properties. The process involves
catalyst preparation followed by a non-agglomerating drying
step.
BACKGROUND ART
Double metal cyanide complex catalysts were discovered in the
decade of the 1960s, and were found to have significant catalytic
activity in a variety of reactions, particularly polymerizations.
Although double metal cyanide salts themselves were found to have
little or no catalytic activity, non-stoichiometric complexes
formed from the double metal cyanide salt and an organic complexing
agent were found to possess high activity. The activity was found
to vary with the identity of the metals contained in the complex,
and also with the organic complexing agents. The chemical makeup,
effects of varying metal ions, and differences in reactivity due to
the complexing agent are discussed in U.S. Pat. No. 3,427,335,
herein incorporated by reference, which further indicates that
polymers of different intrinsic viscosities, and therefore of
differing molecular weight, may be obtained by suitable selection
of organic complexing agent.
According to the '335 disclosure, excess complexing agents can be
removed by extraction with a low boiling, non-complexing solvent
such as pentane or hexane. In a typical laboratory catalyst
preparation, a solution of an alkali metal hexacyanometallate salt,
e.g. K.sub.3 Fe(CN).sub.6 is added slowly to a stirred solution of
metal chloride salt, e.g. zinc chloride, in slight molar excess.
The precipitated zinc hexacyanoferrate(III) salt is washed
thoroughly with water, and then washed with three portions of
anhydrous dioxane. In an optional procedure, the dioxane washed
precipitate is slurried in dioxane/hexane and refluxed, water being
removed as an azeotrope. The moist solid is dried under vacuum of
c.a. 1 torr. The dry catalyst may be crushed to a fine powder.
The catalytic activity of catalysts of the type disclosed by the
'335 patent and other related disclosures such as U.S. Pat. Nos.
3,427,256, 3,427,334, 3,829,505, and 3,941,849, although high, was
not high enough to overcome the high cost of such catalysts
relative to other catalysts traditionally utilized. For example, in
conventional oxyalkylation reactions useful in preparing
polyoxyalkylene polyols and polyoxyalkylene block surfactants,
potassium hydroxide had long been the catalyst of choice due to its
low cost. Moreover, removal of catalyst residues from double metal
cyanide catalyzed polyols also proved to be problematic and to add
additional expense to the production process. As a result, little
if any commercialization of double metal cyanide catalysts of the
types disclosed by the aforementioned patents occurred.
In the 1980's, double metal catalysts were revisited, spurred on in
part by the desire to manufacture polyether polyols with lower
unsaturation and higher equivalent weights. In base catalyzed
polyoxyalkylation, a competing rearrangement of higher alkylene
oxides into unsaturated alcohols continuously introduces
monofunctional, oxyalkylatable species into the oxyalkylation
reactor. For example, propylene oxide, the most widely used higher
alkylene oxide, rearranges to allyl alcohol. Oxypropylation of this
monohydric species results in polyoxyalkylene monols. Continued
generation of allyl alcohol and the continued oxyalkylation of it
and the previously generated and oxyalkylated monols results in a
considerable proportion of monohydric species spanning a broad
molecular weight range.
For example, in the manufacture of polypropylene glycols, the base
catalyzed oxypropylation of a propylene glycol initiator results in
a mixture of polyoxypropylene glycols and oxypropylated allyl
alcohol polymers and oligomers. As oxypropylation continues, the
mol percentage of monofunctional species steadily increases. In a
2000 Da equivalent weight polyoxypropylene "diol," the
monofunctional species content may range between 30 and 40 mol
percent, and the functionality reduced from the "nominal," or
theoretical functionality of 2.0 to an actual, measured
functionality in the range of 1.6 to 1.7. In the case of a 2000 Da
equivalent weight triol, e.g. an oxypropylated glycerine polyol,
the actual functionality will be closer to two than the nominal, or
"theoretical" functionality of three.
Investigations of other catalysts in attempting to lower monol
production during oxyalkylation did not, in general, lead to
commercially acceptable systems. For example, lowering the reaction
temperature during base catalyzed oxypropylation was found to lower
unsaturation, but at the expense of greatly increased process time.
Levels of unsaturation in the range of 0.010 meq/g polyol, as
measured by ASTM 2849-69, "Testing of Urethane Foam Polyol Raw
Materials" could be produced, but with reaction times measured in
days or even weeks rather than typical batch times of 8 to 12
hours. Use of alternative catalysts such as cesium or rubidium
hydroxide (U.S. Pat. No. 3,393,243); strontium or barium oxides
and/or hydroxides (U.S. Pat. Nos. 5,010,187 and 5,114,619); and
alkaline earth metal carboxylates (U.S. Pat. No. 4,282,387) have
all been proposed.
In U.S. Pat. Nos. 4,472,560 and 4,477,589, promoted double metal
cyanide complex catalysts prepared by addition of inorganic acids
or salts such as alkali metal hexafluorosilicates to double metal
cyanide complexes were proposed. The promoter addition takes place
in the presence of excess complexing agent, i.e. glyme, or in the
presence of a liquid initiator, and following dehydration produces
a catalyst/initiator slurry. However, a different slurry must be
prepared for each different initiator desired, and the process
cannot be used to prepare slurries of catalyst in volatile
initiators. Moreover, the catalyst slurries are much more expensive
to ship as compared to dry catalyst. However, the catalysts were
stated to exhibit improved catalytic activity, and were also stated
to be useful at temperatures in the range of c.a. 110.degree. C. to
120.degree. C., while prior DMC catalysts generally were rapidly
deactivated at temperatures in excess of 100.degree. C.
Further improvements in DMC catalysts are evidenced by the
processes of preparation disclosed in U.S. Pat. No. 5,158,922,
wherein modestly heated double metal cyanide-forming reactants, a
relatively large stoichiometric excess of metal salt over metal
cyanide salt, and a specific order of mixing these salts resulted
in greatly improved catalytic activity. Japanese Patent Application
Kokai No. 4-145123 disclosed that use of t-butanol as the organic
complexing agent rather than glyme, the most common complexing
agent, also resulted in improved catalysts, particularly with
respect to catalyst longevity. These improvements, coupled with
improved and less costly methods of removal of catalyst residues
from finished polyether products as illustrated by U.S. Pat. Nos.
4,721,818; 4,987,271; 5,010,047; and 5,248,833, led to
commercialization of DMC-catalyzed polyether polyols for a short
time.
Most recently, discoveries by the ARCO Chemical Co. have resulted
in double metal cyanide complex catalysts which not only offer
polymerization rates which are considerably higher than prior
catalysts, but moreover are far more easily removed from the
polyoxyalkylene polyether product. While earlier DMC catalysts were
able to produce polyols with levels of unsaturation in the range of
0.015-0.020 meq/g, these new catalysts consistently produce polyols
with unsaturation in the range of 0.003 to 0.008 meq/g. Such
catalysts are disclosed in U.S. Pat. Nos. 5,470,813 and 5,482,908,
which are incorporated herein by reference. Double metal catalysts
such as those disclosed by the 5,470,813 and 5,482,908 patents
often allow for catalyst residue removal from polyol product by
simple filtration. Moreover, the catalytic activity is so high in
some cases that the low amounts of catalyst used, e.g. 10-25 ppm,
does not require any removal process.
However, the process of preparing the double metal cyanide complex
catalysts themselves is lengthy, and involves numerous steps. While
the process is easily done on a laboratory scale, on a commercial
scale, catalyst preparation time increases dramatically. For
example, in a commercial scale manufacturing process, catalyst
preparation may consume in excess of 100 hours. Approximately 88%
of this time is consumed in isolating the catalyst solids, drying
the moist filter cake obtained, and grinding the catalyst into
small particles.
Surface morphology may also be of importance with respect to
catalytic activity for double metal cyanide complex catalysts. For
example, in U.S. Pat. No. 5,470,813, unique double metal cyanide
catalysts were produced which differed from prior art catalysts by
being substantially amorphous, rather than possessing significant
amounts of highly ordered or crystalline material. The amorphous
nature of these catalysts was demonstrated by the lack of certain
sharp lines in the X-ray diffraction spectrum which are
characteristic of crystalline double metal cyanide salts.
The substantially amorphous catalysts exhibited surprising and
unexpected increases in catalytic activity, yet the particle size
was actually much larger than that of prior art catalysts, prepared
from similar chemical constituents, which thus presented higher
surface area. The catalytic activity of such substantially
amorphous catalysts can be increased yet further by grinding the
catalyst to smaller particle sizes. Particle sizes less than 10
.mu.m are desired.
The grinding process is very time intensive. Moreover, the moist,
bulk filter cake produced during catalyst preparation retains a
substantial amount of complexing agent, even after considerable
time drying in vacuo. During this intensive grinding, surface
modifications to the catalyst particles due to the inherent nature
of the grinding operation may cause changes in catalytic activity.
Thus, an increase in activity due to smaller particle size may be
offset, at least in part, by a decrease in activity due to changes
in surface morphology. Surface morphology may also affect
properties other than activity per se. For example, double metal
cyanide catalysts produced in finely ground form may also exhibit
reactor fouling, in which gel-like and presumably very high
molecular weight products accumulate in the reactor.
It would be desirable to provide a process by which double metal
cyanide complex catalysts may be prepared with reduced processing
time. It would be further desirable to be able to prepare double
metal cyanide complex catalysts of small particle size without the
risk of altering surface morphology by intensive grinding. It would
be yet further desirable to prepare double metal cyanide complex
catalysts which offer increased handling ease, increased storage
stability, less reactor fouling during polymerization, and higher
catalytic activity.
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that double metal cyanide
complex catalysts having improved catalytic activity, greater
storage stability, and other desirable properties can be produced
in very small particle sizes without intensive grinding, by
slurrying the double metal cyanide complex catalyst into a volatile
complexing agent and removing the excess complexing agent by a
non-agglomerative removal method. As a result of the process, solid
double metal cyanide complex catalysts of fine particle size are
directly obtained. Preferred non-agglomerative methods of excess
complexing agent removal include spray drying and freeze
drying.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE illustrates, in schematic form, a spray dryer useful in
accordance with a non-agglomerative drying method according to the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The double metal cyanide complex catalysts of the subject invention
are non-stoichiometric complexes of a volatile organic complexing
agent and a double metal cyanide salt, optionally containing
activity promoters and optionally containing a further complexing
agent as well. The double metal cyanide salts themselves are well
known to the skilled artisan, and in general contain a negatively
charged complex ion consisting of a first metal ion surrounded by a
plurality of cyanide ions and complexing ligands, and a second
metal cation which at least in part counterbalances the charge of
the complex cyanide anion. Other anions, cations, activating
agents, and the like, may also be present as well. The metals are,
in general, transition metals or inner transition metals. Examples
of double metal cyanide salts include zinc hexacyanocobaltates,
nickel hexacyanoferrates, iron hexacyanoferrates, zinc
hexacyanonickelates, and the like. Further examples of double metal
salts may be found in the previously cited U.S. patents, which have
been incorporated by reference, and in particular by U.S. Pat. No.
5,470,813, 5,482,908, and U.S. application Ser. No. 08/435,116,
which is also incorporated herein by reference.
The volatile organic complexing agent is a heteroatom-containing
organic ligand which can be removed from the double metal cyanide
complex by evaporation. Examples of such organic ligands include
low boiling alkanols, glycols, esters, ketones, nitriles, amides,
ethers, and the like. Examples include isopropanol, 2-butanol,
t-butanol, glyme, diglyme, diglyet, and the many complexing agents
disclosed in the aforementioned patents. The volatile organic
complexing agent is generally used in considerable excess, with
that portion not involved in complex formation being subsequently
removed. More than one volatile complexing agent may be used.
In addition to the volatile organic complexing agent, a
substantially non-volatile complexing agent may be used as well.
The non-volatile complexing agent is one which is oligomeric or
polymeric in nature and generally has little vapor pressure at room
temperature or below. The molecular weight of the non-volatile
organic complexing agent is generally above 300 Da and often
considerably higher, for example in the range of 1000 Da to 10,000
Da. Examples of preferred non-volatile complexing agents include
polyoxyalkylene glycols and polyols, particularly polyoxypropylene
glycols and polyoxypropylene polyols. Particularly suitable are
polyoxypropylene polyols end-capped with isobutylene oxide to
provide tertiary hydroxyl group termination.
A typical laboratory preparation of double metal cyanide complex
catalyst is illustrated by Example 1 of U.S. Pat. No. 5,470,813,
reproduced hereafter.
Laboratory Preparation of Double Metal Cyanide Catalyst
Potassium hexacyanocobaltate (8.0 g) is added to deionized water
(1.50 ml) in a beaker, and the mixture is blended with a
homogenizer until the solids dissolve. In a second beaker, zinc
chloride (20 g) is dissolved in deionized water (30 ml). The
aqueous zinc chloride solution is combined with the solution of the
cobalt salt using a homogenizer to intimately mix the solutions.
Immediately after combining the solutions, a mixture of tert-butyl
alcohol (100 ml) and deionized water (100 ml) is added slowly to
the suspension of zinc hexacyanocobaltate, and the mixture is
homogenized for 10 minutes. The solids are isolated by
centrifugation, and are then homogenized for 10 minutes with 250 ml
of a 70/30 (v:v) mixture tert-butyl alcohol and deionized water.
The solids are again isolated by centrifugation, and are finally
homogenized for 10 minutes with 250 ml of tert-butyl alcohol. The
catalyst is isolated by centrifugation, and is dried in a vacuum
oven at 50.degree. C. and 30 in. (Hg) to constant weight.
In the foregoing example, less than 10 g of catalyst is produced.
Isolation of catalyst solids from the slurry of catalyst in
t-butanol is performed in a laboratory centrifuge. The moist
centrifuge cake is then dried under vacuum.
The standard laboratory techniques illustrated in the laboratory
catalyst preparation are more difficult to implement on an
industrial production scale. For example, the initially produced
catalyst solids in the catalyst slurry are of a particle size which
does not lend itself to isolation by filtration. For isolation by
centrifugation, large and expensive centrifuges, e.g. a high
rotation solid ejecting centrifuge, must be used. For drying the
moist centrifuge cake or pellets obtained, numerous types of vacuum
driers may be used. However, most are bulky and expensive batch
driers, which seal with some difficulty, and which do not always
offer either the desired rate of heat transfer or obtainable
vacuum. For example, in the industrial preparation of approximately
135 Kg of catalyst, a 7,000-8,000 l batch reactor is required. The
total process time will vary with the particular mode of catalyst
preparation, for example with the number of wash and complexing
steps, activating agent addition steps, etc. In a typical process,
precipitation, washing, and isolation consumes approximately 84
hours, while drying and grinding consume an additional 24 hours,
for a total cycle of approximately 108 hours. Thus, a considerable
portion of the total time is directed to drying and grinding
operations, while a further considerable portion involves isolation
by centrifugation prior to drying. In the present process, the
pre-drying centrifugation, moist centrifuge cake drying, and
grinding operations are replaced by a non-agglomerative drying
step. As a result, the process time is much shorter. A typical
process utilizing spray drying as the means of catalyst
isolation/drying consumes only about 76 hours.
The spray drying step has been found to produce catalyst with
particle sizes less than 10 .mu.m, thus rendering grinding
unnecessary. The modified process saves 32 hours (4 shifts) of
production time, and the cost of catalyst is greatly reduced as a
result. However, it has been surprisingly found that the catalyst
produced has higher catalytic activity, produces polyoxyalkylene
polyols with less unsaturation, and importantly, with less reactor
fouling than compositionally similar catalysts produced in the
conventional manner. These results are completely surprising and
unexpected. Due to the greater dryness, the storage stability is
expected to be higher, as is also the ease of handling and
packaging.
As used herein, the terms "drying" and "moist" are not used in the
same sense as in other areas of technology as pertaining to water
content. Water is substantially removed from the double metal
cyanide salt by the first centrifugation and successive washes with
complexing agent(s) which serve(s) to dehydrate the double metal
cyanide salt as well as complex with the salt. Rather, the terms
"dry," "drying," "moist" and "wet" refer in the present invention,
to catalyst containing liquid other than water.
For example, in the conventional preparation of zinc
hexacyanocobaltate-glyme complexes, the "moist" nature of the
centrifuge cake is due to the presence of glyme beyond that which
is involved in the formation of the complex. With t-butanol
complexed catalysts, the presence of additional t-butanol produces
the same effect. Following vacuum drying of moist centrifuge cake
in the conventional process, a product which appears to be dry is
obtained. This product can be easily crushed to powder. The
majority of glyme or t-butanol still contained in the powdered
catalyst is chemically bound in the double metal cyanide complex.
However, a small proportion of complexing agent is still believed
to be retained in non-bound form.
The initial catalyst complex preparation may be performed in
numerous manners. For example, the salt solution, i.e. aqueous zinc
chloride, may be added to the complex salt solution, i.e. aqueous
potassium hexacyanocobaltate, organic complexing agent added, the
solids isolated by filtration or centrifugation and reslurried in
additional or different complexing agent. Alternatively, and
preferably, the organic complexing agent is present at the time the
two salts are first contacted, i.e. by adding the organic
complexing agent to the potassium hexacyanocobaltate solution prior
to adding the zinc chloride solution to it. Most preferably, the
mixing is by high shear stirring, impingement mixing,
homogenization, and the like.
Following initial preparation of the solid catalyst, the mother
liquor is removed by filtration and/or centrifugation, and the
catalyst is generally washed with water or water/complexing agent
and/or reslurried in fresh complexing agent(s). This reslurrying
may not always be necessary, but is generally desirable to produce
catalysts of the greatest activity. The separation/reslurrying is
generally performed twice, and may be performed numerous times.
During the wash/reslurry process, substantially all water is
removed from the catalyst. It may be appropriate at this time to
add a second complexing agent, for example a polyoxypropylene
polyol. Although such higher molecular weight complexing agents are
generally only of limited solubility in water, many are of much
higher solubility in lower molecular weight complexing agents such
as glyme and t-butanol.
The present process avoids collection of the completed catalyst as
a moist cake, whether by filtration, centrifugation, or other
liquid/solid separation method. Rather, the completed catalyst is
maintained in its last slurried or dispersed form, and subjected to
a non-agglomerative drying process. In the sense used herein,
"completed catalyst" refers to the catalyst at the point where all
chemical modifications, i.e. washing, complexing, etc., have been
completed, and catalyst isolation in dry form remains to be
accomplished.
By "non-agglomerative drying" is meant a drying process in which
particle agglomeration is substantially prevented. For example,
examination of the catalyst particle size in a wet centrifuge cake
indicates that the median particle size may be 1.5 .mu.m. However,
after drying such a cake in the conventional manner, i.e. vacuum
drying, the resulting particle size is much larger. A 135 Kg batch,
for example, requires about 12 hours of intensive grinding to
obtain a median particle size less than 10 .mu.m. Thus, during the
drying stage, considerable particle agglomeration has occurred. By
"non-agglomerative drying" is meant a drying process other than
conventional vacuum drying of an isolated solid product such that
significant agglomeration is prevented, and a powdered product of
fine particle size may be directly obtained.
In many such non-agglomerative methods, particle to particle
contact is minimized. In others, for example fluidized bed drying,
Therma Jet.TM. flash drying, vacuum stripping with plough and
ribbon, or other similar methods, particle-to-particle contact
occurs, but the manner and/or duration of contact prevents
agglomeration. Preferably, the powdered catalyst isolated from such
a method has a particle size less than 40 .mu.m, more preferably
less than 20 .mu.m, and most preferably about 10 .mu.m or less, all
without grinding. Most preferably, the particle sizes obtained from
the non-agglomerative drying method will be of the same order of
magnitude as those which would otherwise be contained in a wet
filter cake obtained by centrifugation. Non-agglomerative processes
which do not produce the smallest particles may require some
grinding. However, the amount and intensity of grinding will be far
less than that required when agglomerative drying operations are
utilized, and any change in surface morphology accordingly
minimized. Preferably, the non-agglomerative drying methods include
spray drying and freeze drying.
In both spray drying and freeze drying, the double metal cyanide
complex particles are isolated from other particles by a separating
matrix. In the case of spray drying, the separating matrix is hot
gas into which the catalyst/complex slurry is atomized. In a
suitable spray drying apparatus, the dryer is constructed so as to
allow the safe spray drying of organic substances. For example, the
process may employ nitrogen or other substantially inert
atmosphere, and may also be operated at reduced pressure. An oxygen
analyzer at the dryer outlet can be used to ensure that oxygen
concentration is below the limit of flammability. The feed to the
dryer can be shut off manually or automatically if the oxygen
concentration exceeds desired limits. In the case of freeze drying,
the separating matrix is additional, non-chemically bound
complexing agent and/or solvent. In both cases, as the complexing
agent and/or solvent is removed, there is minimal contact of double
metal cyanide complex particles, and particularly, little
pressurized contact. Thus, very little agglomeration occurs.
BRIEF DESCRIPTION OF THE DRAWING
A pilot scale spray drying apparatus is illustrated by FIG. 1.
DETAILED DESCRIPTION OF THE DRAWING
The double metal cyanide complex catalyst slurry 1 is contained in
slurry feed tank 2 and pumped from the slurry feed tank to the
inlet 5 of spray dryer 7 by a feed pump 3, which may be of the
peristaltic type or other type. As the catalyst slurry passes
through supply line 9, it may optionally be heated or cooled.
Nitrogen or other relatively inert gas is fed through line 11
through regulator 12 to atomizing gas inlet 13 of spray dryer 7.
The atomizing gas pressure and volume, the catalyst slurry feed
rate, and the size and geometry of atomizing nozzle 15 of atomizer
17 are adjusted to produce the desired degree of atomization. It is
currently believed that a higher degree of atomization and a more
dilute catalyst slurry both minimize agglomeration, and lead to
finer particle sizes. The atomizer, nozzle, etc., may take numerous
forms. For example, an atomizing nozzle which does not employ gas
to assist in atomizing may be used. In lieu of an atomizer of the
types previously described, a spinning disk atomizer, where a
stream of catalyst slurry impinges upon a rapidly spinning disk may
be used to implement atomization.
Heated drying gas is fed from source 16 through pressure regulator
17 through a heater 19 to supply heated gas to spray dryer 17
through drying gas inlets 18. From the spray dryer, the dried
particulate catalyst passes to cyclone 21 where it is separated
from the hot, vapor laden gas. Product 22 is collected in drums,
cans, or other appropriate product collection containers 23.
Organic complexing agent/solvent vapors pass through filter 25 to
cold trap 27, which may be maintained at 0.degree. C. in an ice
bath, or cooled to an appropriate temperature by a refrigerating
device 28. From the cold trap 27, the vapors pass to a further cold
trap 29 maintained at lower temperature by device 30. Aspirator
pump 31 ensures mass flow in the proper direction. The pump output
may be adjusted to enable operation at less than atmospheric
pressure, which is preferred.
Commercial spray dryers are readily available, and are commonly
used for spray drying instant coffee, instant tea, dyes and
pigments, synthetic elastomer particles, etc. The theory and
operation are well known, and need not be described here. On a
commercial scale, the ice bath and dry ice cold traps would likely
be replaced by refrigerated units. Parameters such as gas flow,
temperature, degree of atomization, slurry input rate and
concentration, etc. can all be adjusted. The process has not been
optimized, but as can be seen from the actual example, the
non-optimized process already produces a surprisingly superior
catalyst.
Freeze drying is a further non-agglomerative means of drying
catalyst in accordance with the subject invention. In the freeze
drying process, solids, as a dispersion or dissolved in a liquid
continuous phase or solvent, in this case complexing agent and/or
solvent, are frozen, following which the normally liquid continuous
phase or solvent is removed by sublimation at reduced pressure.
Freeze drying has an advantage in that it avoids the higher
temperatures associated with spray drying and other drying methods.
For this reason, freeze drying is commonly used for temperature
labile products such as biochemicals, pharmaceuticals, and the
like. Freeze drying has been used for many years for the freeze
drying of instant coffee.
Freeze drying may be accomplished in a batch or continuous process.
In continuous processes, the composition to be freeze dried must
traverse a freeze drying chamber having means to seal the entry and
exit so as to maintain suitable vacuum. In batch-type processes,
the composition may be placed in metal trays in a vacuum chamber,
frozen, and sublimed. In either case, the time in which freeze
drying is accomplished is minimized by maximizing surface area of
the frozen composition. The freeze drying process and equipment for
its use are well known to those skilled in the art of freeze drying
equipment.
Having generally described this invention, a further understanding
can be obtained by reference to certain specific examples which are
provided herein for purposes of illustration only and are not
intended to be limiting unless otherwise specified.
EXAMPLE 1
Catalyst Preparation
A solution of 7.5 g potassium hexacyanocobaltate dissolved in 300
ml distilled water and 50 ml t-butanol was introduced into a 500 ml
beaker. In a separate beaker, 75 g zinc chloride was dissolved in
75 ml distilled water. The solution of zinc chloride thus prepared
was added to the potassium hexacyanocobaltate solution over a
period of 30 minutes at 30.degree. C. with intensive mixing using a
Power-Gen.TM. homogenizer set at a 20% power level. Following
completion of addition, the mixing intensity was increased to 40%
and mixing continued for 10 minutes. The solids were then isolated
by centrifuging at 17,000 rpm for 30 minutes. The centrifuge cake
was reslurried in 155 ml t-butanol and 55 ml distilled water in a
500 ml beaker and homogenized at 40% power level for 10 minutes.
The solids were isolated by a centrifugation as previously done,
and then reslurried in 185 ml t-butanol at a 40% power level for 10
minutes. The centrifuge cake was divided into two halves. The first
half (Catalyst A), was dried at 60.degree. C. under 30 in/Hg vacuum
until a constant weight was obtained. The catalyst was then crushed
into fine powder. The second half of the isolated moist cake was
reslurried into 1,000 ml t-butanol at 25% homogenizing power for 10
minutes. This slurry was frozen in an ice bath and then freeze
dried under vacuum. A fluffy powder catalyst was obtained directly.
This freeze dried catalyst is denoted as Catalyst B.
EXAMPLE 2 AND COMPARATIVE EXAMPLE C2
Polyol Synthesis
The catalysts prepared in Example 1 were used to prepare 8,000 Da
polyoxypropylene diols. A one liter stirred reactor was charged
with catalyst (0.0166 g, 25 ppm relative to finished polyol) and a
785 Da molecular weight polyoxypropylene diol (65 g) prepared
conventionally from propylene glycol, KOH, and propylene oxide was
used as the initiator molecule. The mixture was well stirred and
heated to 105.degree. C. under vacuum for about 30 minutes to
remove traces of residual water. The reaction temperature was
increased to 130.degree. C., and approximately 11 g of propylene
oxide added to increase the pressure in the reactor from vacuum to
about 2 psig.
An accelerated pressure drop was noted, indicating the catalyst had
become active. After catalyst initiation was verified, additional
propylene oxide (600 g total) was continuously added at a rate of
approximately 1.7 g/min over 6 hours. The reactor was held at
130.degree. C. for 30-45 minutes until a constant pressure was
obtained, which indicated that propylene oxide conversion was
complete. The mixture was stripped under vacuum at 60.degree. C.
for 30 minutes to remove traces of unreacted propylene oxide. The
product was cooled and recovered and its properties measured. The
properties of the polyols prepared from Sample A and Sample B
catalysts of Example 1 are presented in Table 1 below.
TABLE 1 ______________________________________ Catalyst A Catalyst
B Catalyst: (Conventionally Dried) (Freeze Dried)
______________________________________ Polyol Properties Hydroxl
No. 14.6 15.0 Unsaturation (meq/g) 0.0067 0.0061 Polydispersity,
M.sub.w /M.sub.n 1.23 1.19 Viscosity, cps, 25.degree. C. 4150 3940
Gel Formation? Yes No ______________________________________
As can be seen, the freeze dried catalyst of the subject invention
are capable of producing polyols with lower unsaturation, lower
polydispersity, and lower viscosity, while not producing reactor
fouling. These results are totally unexpected and surprising.
EXAMPLE 3
Spray Dried Catalyst Preparation
A double metal cyanide catalyst is prepared substantially in
accordance with Example 1, however, following reslurrying of the
centrifuge cake in t-butanol, the slurry is divided into two parts.
The first part is centrifuged and dried in the conventional manner,
and is identified as Catalyst C. The second portion is introduced
into a pilot plant scale spray drier as illustrated in FIG. 1,
employing a feed rate of 10 ml/min of catalyst slurry.
Approximately 7.5 liters/minute of nitrogen heated to a temperature
of 106.degree. C. is used to dry the atomized catalyst slurry. The
catalyst is collected from a cyclone, and its particle size and
activity measured. Also measured are the catalyst particle sizes in
the undried, wet centrifuge cake obtained from the first portion of
the slurry (Catalyst C). Particle sizes were measured by
conventional light scattering techniques in a Microtrac Full Range
Particle Size Analyzer by volume distribution. The particles in the
wet cake and the spray dried particles were found to have the
particle sizes indicated in Table 2 below. The particle sizes
reported herein are in .mu.m (microns).
TABLE 2 ______________________________________ Sample Particle Size
(.mu.m) Distribution Description 10% 50% 90%
______________________________________ Spray Dried 1.03 2.93 9.56
Final wet cake 0.65 1.50 3.10 Conventionally Dried 15.22 127.04
326.32 and Ground Wet Cake
______________________________________
As can be seen from the table, very little agglomeration occurred
during the spray drying process over what was the particle size
contained in the final wet cake. In contrast, during conventional
vacuum drying of the wet cake, considerable particle agglomeration
takes place resulting in the necessity of prolonged grinding to
obtain a reasonable particle size. The spray dried particles have a
median size of 2.93 microns as obtained from the spray drier.
EXAMPLE 4 AND COMPARATIVE EXAMPLE 4
Two 6000 Da polyoxypropylene triols were produced by oxyalkylating
an oligomeric oxypropylated glycerine starter using the spray dried
catalyst of Example 3 and the comparative catalyst prepared by
conventional vacuum drying. The rates of oxypropylation, the
unsaturation of the polyoxypropylated triol product, and degree of
reactor fouling were noted. The results are presented in Table 3
below.
TABLE 3 ______________________________________ 4C 4 Example
Catalyst C Catalyst D Catalyst (conventional) (spray dried)
______________________________________ Reaction rate (g PO/min)
20.0 21.7 Unsaturation meq/g 0.0034 0.0032 Reactor Fouling mild
none ______________________________________
As can be seen, the spray dried catalyst offered a slightly higher
reaction rate, lower unsaturation, and eliminated reactor
fouling.
EXAMPLES 5 AND C5
The procedure of Example 2 is followed to prepare 8000 Da
polyoxypropylene diols using the spray dried, and conventionally
dried catalysts of Example 3. The viscosity and unsaturation are
indicated in Table 4 below.
TABLE 4 ______________________________________ Example 5C 5
Catalyst Catalyst C Catalyst D
______________________________________ Diol Viscosity (cps) 3750
3780 Unsaturation 0.0071 0.0051
______________________________________
The viscosities of the polyol products are virtually identical,
however the unsaturation of the polyol produced using the spray
dried catalyst is considerably lower at 0.0051 meq/g as compared to
0.0071 meq/g for the conventionally dried catalyst.
Having now fully described the invention, it will be apparent to
one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
or scope of the invention as set forth herein.
* * * * *